Percentages: GCSE Maths revision
Percentages are hundredths. GCSE papers test percentage of an amount, increase and decrease, reverse percentages, and compound interest.
Multiplier method
A 20% increase uses × 1.20. A 20% decrease uses × 0.80. Compound interest for n years: × (1 + r)ⁿ.
A jacket costs £40. Increase by 15%.
Reverse percentages
If a price is £36 after a 20% increase, that £36 is 120% of the original. Divide by 1.20.
After 20% off, a game costs £24. Original price?
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
Find 35% of 80
Increase 50 by 12%
A £200 bike is reduced by 15%. New price?
After a 10% increase a bill is £55. Original bill?
£1000 at 3% compound interest for 2 years.
Common mistakes
- Treating reverse percentages as “subtract 20% of the new amount”.
- Using simple interest when the question says compound.
Answers and working
Frequently asked questions
What is a multiplier?
A single number you multiply by to apply a percentage change, e.g. 1.03 for a 3% increase.
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